Synapsida

Sunday, 20 May 2018

By some definitions, the term "pig" can really only be applied to those species that are most closely related to the domestic animal; those included within the genus Sus. This includes the wild boar, and the various kinds of warty and bearded pig that inhabit the Indonesian and Philippine islands.

But these are not the only pig-like animals to inhabit Asia. In 1847, Brian Hodgson, a naturalist and former colonial administrator who was living in Darjeeling at the time, described and named the pygmy hog (Porcula salvania), an animal he considered so different from regular pigs in the shape of its teeth and feet that he placed it in its own, newly defined, genus, Porcula. (The scientific name, incidentally, translates as "piglet from the Sal Van", the latter being a forest that only coincidentally sounds like the Latin "silvae" meaning "woodland").

Sunday, 13 May 2018

As the climate cooled around 11 million years ago, the forests of Europe began to thin out once more, something that favoured fast-running animals such as horses. Until this time, the only kind of horse in Europe, however, was the small, three-toed, Anchitherium, which was likely adapted to dense woodland and not so suited to the new climate. Its own ancestors had reached the continent from the east, having crossed over during one of the periodic rises of the Bering Land Bridge, but now, not coincidentally, given the colder climate, the Land Bridge rose again, and a second kind of horse followed it out of the Americas.

Sunday, 6 May 2018

Cetaceans (whales, dolphins, and porpoises) are the best adapted of all mammals to life underwater. Their food is often found far below the waves, requiring them to dive deep to find it. But this, of course, is countered by the fact that, not being fish, they also have to return to the surface to breathe. The deeper the desirable food happens to be, the longer they will have to dive for just to reach it, and the longer they will have to spend recovering on the surface afterwards - even if the actual feeding time remains the same.

Such pay-offs are arguably particularly important for the huge rorqual whales, which feed by lunging at great masses of krill or other small prey and gulping them down. For them, it really matters that wherever they are diving is rich in food, so that they can find enough to offset the effort required to catch it. Quite how they strike that balance should depend on how good they are at diving, which relates to things such as their lung capacity and how much oxygen they need to sustain their bodies.

Sunday, 29 April 2018

At least if you live in the northern, temperate, parts of the world, when you think of where to find bats, your first thought is likely to be "caves". A great number of bat species do, indeed, spend the day in caves, and this makes sense: if you're a nocturnal animal that doesn't need light to 'see', then caves are both reasonably safe places and ones with a constant, sheltered environment. Why bother trying to sleep in the wind and the rain, or even the bright sunshine, when you don't have to?

But, of course, by no means all bats are cave-dwellers. Amongst the various families of bat, the leaf-nosed bats (Phyllostomidae) of the American tropics are the most varied in terms of diet, and also in terms of their roosting habits and other behaviour. Sure, the majority of phyllostomid species do eat insects and live in caves, as most other bats do. But the group also includes some bats that feed on surprisingly large prey (such as birds) as well as the blood-drinking vampire bats.

It also includes a large number of species that are vegetarian, feeding on fruit such as figs, or subsisting almost entirely on the sugar-rich nectar that they drink from year-round tropical flowers. Many of these fruit-eating species do not live in caves at all, but simply roost in trees - as do the much larger fruit bats of the Old World

Sunday, 22 April 2018

When the animal we now know as the Sulawesi warty pig was first described, back in the 19th century, it was thought that it lived, not only on the island of Sulawesi, but also on a whole chain of islands to the north - the Philippines. But the pigs there didn't look exactly the same as those to the south, so in 1886, German zoologist Alfred Nehring proposed that they be regarded as a distinct subspecies.

And so things remained for a hundred years, until scientists began to look more closely at the animal's genetics. When they did so, they discovered something fairly surprising. Pigs typically have 38 chromosomes (compared with 48 in humans), but it turned out that the warty pigs from the Philippines had only 36 - an entire pair had disappeared, its genetic material shuffled around elsewhere in the genome.

Sunday, 15 April 2018

We tend to think of rodents as small mammals, and the great majority of them are: mice, voles, hamsters, tree squirrels, and so on. Even rats and gophers aren't really all that big. Indeed, when most people think of rodents they probably aren't mentally including the largest ones, such as porcupines and beavers. In fact, the very largest rodent alive today is the capybara, a sort of giant guinea pig that is around 120 cm (4 feet) long and weighs something like 50 kg (110 lbs).

This, you probably won't be surprised to learn, is as nothing compared to some of the fossil species.

Sunday, 8 April 2018

Even in mammals that are otherwise social, it is quite common for males and females to live apart for most of the year. The most common pattern involves females living in groups with their children, until the latter approach adulthood, while males either live alone, or in much smaller bands, outside of the mating season. In many hoofed herd animals, however, the males live in herds that aren't much smaller than those of the females - in other words, both sexes live in herds, but the two don't mix until it's time to do the necessary.

Clearly, these are creatures that benefit from the group protection that living in herds provides, and, while there's obviously a limit on how large a herd can be before there isn't enough food to support them all, it's not always so clear why the herds should be single-sex. Why, in short, do so many hoofed herd animals practice sexual segregation?

There are a number of theories, and, as is often the case, they aren't mutually exclusive. Nor is it likely that the reason - or the balance of reasons, if there's more than one - will be the same for every species. It's something we have to examine on a case-by-case basis.